@CelloMomOnCars NOx are a problem with all types of internal combustion engines. The higher the efficiency, the higher the NOx production. However, the technology to remove them exists.
I wouldn't worry too much about the toxicity. NH3 has a strong smell, so it would not go unnoticed. As I said, hundreds of megatonnes of NH3 are already produced and transported everyday w/o major problems. In an industrial environment, NH3 can be handled easily. It is far less toxic than e.g. Silane (H4Si).